Yearn for a tree (4)
I believe the answer is:
pine
I believe this clue is a double definition.
'yearn' is the first definition.
(I know that pine is a more specific form of the action the yearn)
'tree' is the second definition.
(I know that pine is a type of Pinophyta)
'for a' is the link.
(Other definitions for pine that I've seen before include "Yen - tree" , "Long - tree" , "Thirst" , "type of wood" , "A tree to grieve for" .)